1. Field of the Invention
The invention relates to methods for collecting and analyzing exhaled breath samples for trace compounds, and devices, apparatuses, and systems for performing such methods.
2. Description of Related Art
Exhaled breath of individuals with some diseases contains distinctive gases, or alveolar gradients compared to air, which differs markedly from the exhaled breath of healthy individuals, i.e. acetone in the breath of individuals with diabetes (Phillips 1992). In addition, because of the high systemic blood flow to the lungs, ingested substances and/or therapeutic drugs are able to partition across the liquid/gas interface and exhaled proportional to systemic levels, i.e. alcohol. Detection of inflammatory markers in the diagnosis of several pulmonary diseases, such as asthma and chronic obstructive pulmonary disease (COPD), could substantially improve the understanding of the pathogenesis of these diseases, improve diagnosis, and identify the efficacy of different therapies. Although progress over the last decade has improved monitoring of forced expiratory volume (FEV) and spirometry, as well as exhaled carbon dioxide and nitric oxide (Montuschi, Kharitonov et al. 2001), these markers tend to vary greatly from patient to patient. Preliminary studies measuring levels of recently identified inflammatory markers in the exhaled breath such as ethane and 8-isoprostane using gas chromatography/mass spectrometry (GC/MS) has shown higher magnitude differences in exhaled levels of COPD patients (ethane 2.77+/−0.25 ppb and 8-isoprostane 40+/−3.1 pg/ml in breath condensate) compared to healthy patients (ethane 0.88+/−0.09 ppb and 8-isoprostane 10.8+/−0.8 pg/ml in breath condensate), suggesting exhaled volatile organic compounds (VOCs) may provide improved markers of COPD and other conditions compared to exhaled NO, CO2, and H2O2 (Montuschi, Collins et al. 2000; Paredi, Kharitonov et al. 2000). Exhaled VOC profiles have provided a link to other diseases where high levels of oxidative stress markers are present, including lung cancer, liver disease, inflammatory bowel disease, rheumatoid arthritis, and schizophrenia (Phillips, Erickson et al. 1995; Phillips, Herrera et al. 1999; Phillips, Cataneo et al. 2000). Results of several studies have also shown that Pseudomonas, Klebsiella pneaumoniae, Proteus mirabolis, Staphylococcus aureus, Enterococcus, Clostrdium, and E. coli emit volatile compounds into the headspace of cultures, also suggesting that diagnosis of patients with these diseases could be performed from monitoring compounds in the breath (Larsson, Mardh et al. 1978; Labows, McGinley et al. 1980; Pons, Rimbault et al. 1985; Zechman, Aldinger et al. 1986; Yu, Hamilton-Kemp et al. 2000; Aathithan, Plant et al. 2001).
Unfortunately, progress in breath testing for various diseases and drug monitoring is hindered by the technical difficulty of detecting very low concentrations of exhaled compounds in the breath (nanomolar or picomolar concentrations). Research has been reported using breath sampling using large heated tubes (Phillips 1995) and cylindrical (Lewis, Severin et al. 2001) containers to collect desired portions of the breath for sampling. Unfortunately, these systems require power for pumping and temperature control limiting their widespread use. Detection of compounds in the collected breath sample has been described using gas chromotography coupled with mass spectrometry (GC/MS), which are sensitive and selective but also bulky and complicated, as well as polymer-coated resistor arrays, which have low sensitivity and are not selective with complex mixtures such as the breath, have both been described (Phillips 1997; Lewis, Severin et al. 2001). In addition, a GC system for detection of volitile compounds in the breath has also been described with improved sensitivity and selectivity that utilizes breath collection on a absorbent sample tube and a second chromatography column for separation of compounds (Satoh, Yanagida et al. 2002). Unfortunately, though, there are no currently available portable vapor or gas sensor systems that can collect and detect mixtures of volatile compounds at low levels in breath, as well as separate compounds from the large exhaled water content. What is desired is an optimized sample collection system and superior detection capabilities. In addition, it would be beneficial if sample collection system and the detection system were small in size, ideally hand-held or portable, without compromising sensitivity and selectivity of the compound of interest for detection.